(1) Field of the Invention
The present invention relates to a method for detecting energy interference in an optically synchronized safety detection system for sliding elevator doors and compensating for such interference.
(2) Description of Related Art
In optically synchronized elevator detection and safety systems, consisting of separate emitter and receiver arrays, the energy produced by an emitter array is produced in a fixed sequence or pattern, and the receiver array predictively enables or activates individual receivers according to the fixed sequence produced by the emitters. When an activated receiver detects sufficient energy from the emitter array, a “connect” is logged for the individual beam being sampled (composed of the specific emitter and its corresponding receiver). The receiver array then disables the currently enabled receiver and activates the next receiver in the scanning sequence. This process continues as long as beams connect. Broken beams (those for which an individual receiver does not detect emitted energy within a specified maximum wait time) cause the detection system to signal a door controller to reopen the doors due to the detection of an obstruction in the path of the closing doors.
A drawback of one such optically synchronized detection system is the potential presence of various external sources of light energy or electrical noise which can interfere with the optical and synchronization, or sync, functionality of the scan. If the energy produced by these external sources is modulated similarly to the energy transmitted by the door safety system, the external energy can be received by the system and interpreted as detection scanning beam energy produced by the emitter array and cause false indexing of receivers to check the next beam in the scan sequence.
Such false indexing causes loss of sync between the emitter array and the receiver array, resulting in false obstruction detections and false reversals of the elevator doors. Sources of interference light energy include fluorescent lighting systems, strobe lights associated with fire alarm systems, and beacons atop emergency vehicles. Sources of external, impulse type, electrical noise include relay type elevator controllers and electromechanical door operators.
What is therefore needed is a safety detection system for sliding doors which ensures proper operation of in the presence of impulse type electrical noise and light sources, which produce light similar to that produced by the safety detection system for scanning purposes.